There is a service in which the communication quality is measured by capturing packets between pieces of apparatus and classifying the response time on each factor basis and a bottleneck in the response time is identified. For example, monitor apparatus is set between a client terminal and a Web server and the response time from click operation of Web screen display to the Web screen display is measured. Then, the monitor apparatus identifies a bottleneck in the response time by classifying the response time into the server processing time, the client processing time, and the transfer time. The transfer time includes the time it takes to transfer data on a network and the retransmission time from the occurrence of packet loss to transmission of a retransmission packet. As a related art, International Publication Pamphlet No. WO 2012/066824 and so forth are disclosed.
If the transfer time is identified as the bottleneck, determination of whether or not the cause thereof is based on transmission of a retransmission packet is carried out. The retransmission time may be calculated based on the time when a lost packet has been captured and the time when the retransmission packet has been captured. However, regarding a packet lost before passage through the monitor apparatus, the lost packet is not captured and only the retransmission packet is captured and therefore it is difficult to calculate the retransmission time.
If a packet is lost on the transmitting side relative to the monitor apparatus, the lost packet is not captured. For this reason, it is also conceivable that the sequence number is utilized and the arrival time of the lost packet is assumed and calculated from the arrival time of packets previous and subsequent to the lost packet. However, with this method, if data such application data is divided into plural packets to be transmitted, an error in the retransmission time becomes large depending on where the lost packet is located in the data and the reliability is low. In view of the above, it is desirable that the retransmission time of the lost packet may be calculated with a small error.